1. Technical Field of the Invention
The present invention relates to the location of a remote mobile unit, and more particularly, to a system enabling location of a mobile unit using FM, AM or TV signals transmitted from known locations.
2. Description of Related Art
As cellular telephones become more widely used by the public, there arises the need to be able to develop information about the location of the cellular telephone so that this may be provided to a cellular base station serving the cellular telephone. By knowing the position of the cellular telephone a variety of different services may be provided to the user, such as providing directions to a selected site, sending emergency services to a user that may be in need of assistance, etc. The problem with acquiring location information arise from the increased cost, size and power consumption requirements for a cellular telephone.
One solution to the problem has been the use of time-of-arrival (TOA) techniques used in conjunction with existing cellular telephone base stations. The problem with time-of-arrival techniques using existing cellular telephone base stations arises from the uncertainty that a sufficient number of base stations will be present to provide the ability to perform triangulation calculations enabling determination of the location of a mobile unit. If sufficient base stations are not present, results may not be calculated and location information is temporarily unavailable. An alternative solution involves the use of global positioning systems (GPS). GPS systems, while effective, have limited sensitivity and may not work in all required environments particularly inside many buildings. These factors limit GPS for location to vehicular, rural and suburban environments.
Since a great deal of cellular telephone usage involves operating a mobile unit within a building or other structure, the ability to calculate location information for a mobile unit located within a structure is necessary. Thus, a need for providing improved location capability for a mobile unit that does not drastically increase the costs, size and power consumption of the unit is greatly desired.